Release liner for pressure sensitive adhesives

ABSTRACT

A release liner for use with a pressure sensitive adhesive. The release liner includes a film of a thermoplastic elastomeric olefin.

This application is a divisional of U.S. Ser. No. 08/929863, filed Sep.15, 1997, now allowed, the disclosure of which is herein incorporated byreference.

FIELD OF THE INVENTION

This invention relates to a release liner for pressure sensitiveadhesive articles.

BACKGROUND OF THE INVENTION

Currently, many pressure-sensitive adhesive tapes and otherpressure-sensitive adhesive-coated articles have a release liner appliedto the adhesive during or following manufacture. For example, therelease liner can serve as a carrier for a pressure sensitive adhesivetransfer tape or a double-coated tape, both of which are tacky on bothsides of the tape. The adhesive tape on a release liner is typicallysupplied on a convolutely wound roll, and then unwound and laminated toan article or substrate. The release liner is typically left in placewhile the article is converted, packaged, and shipped to ultimate users,and in many instances is left in place until the article is bonded toand adhered to another substrate with the pressure-sensitive adhesive.Release liners are used for one or more of a number of purposes,including, for example, preventing contamination of the adhesive layer,facilitating handling of the adhesive-coated article (e.g., by providingsupport thereto as well as covering the adhesive), identifying thearticles to which they are applied, etc.

The type of adhesive is typically matched to the type of release liner.For example, state-of-the-art release liners for acrylicpressure-sensitive tapes are polyethylene or polypropylene films. Thesefilms have been successfully used for acrylic pressure-sensitiveadhesives for many years because they do not require a separate coating(e.g. silicones) to provide a release surface. Silicone-coated polyesterrelease liners are also well-known in the art.

Conventional polyolefin-based or polyester release liners that functionwell at ambient temperatures are, however, often unsuitable for use inmanufacturing processes that involve heating and cooling a substrateafter application of an adhesive tape but before removal of the releaseliner. For example, during the painting process, painted thermoplasticautomobile parts are typically exposed to temperatures of about 250° F.or higher for extended periods of time to cure the paint and thencooled. It is often desirable to apply an adhesive tape with a releaseliner to an unpainted substrate, paint the substrate and cure the paintat high temperature, then remove the release liner after cooling.Polyethylene release liners, however, cannot withstand high temperaturesused in paint curing ovens and can melt, shrink or buckle duringprocedures that involve heating and cooling. Silicone-coated polyesterliners can withstand high temperatures, but are also unsuitable forapplications that involve thermal cycling because they do not expand andcontract at the same rate as thermoplastic polyolefin substrates whenheated and cooled, and the polyester liners tend to pull away from theends of the adhesive tape upon heating or buckle upon subsequentcooling.

What is needed in the industry is a release liner for pressure sensitiveadhesives, particularly for acrylic foam tapes, that is suitable for usein manufacturing applications that involve heating and cooling of asubstrate.

SUMMARY OF THE INVENTION

The present invention provides a release liner for pressure sensitiveadhesives articles such as single- or double-sided tapes, films, labels,and the like. The release liner of the present invention comprises athermoplastic elastomeric olefin (TEO). TEO imparts thermal stability tothe liner so that it is not likely to significantly decompose or meltwhen exposed to elevated temperatures during manufacturing andprocessing of a typical substrate to which it is applied. The use of TEOin the release liner also decreases the likelihood that the liner willshrink away significantly from the adhesive upon heating, orsignificantly buckle upon cooling. The release liner of the presentinvention is thus especially suitable for, although not limited to, usein manufacturing processes conducted at elevated temperatures,particularly those that involve heating to temperatures, such asexposure to temperatures of about 90° C. to about 150° C. for periods ofup to one-half hour or one hour or more, followed by cooling to roomtemperature (i.e., about 20° C. to about 25° C.).

Preferably the release liner is a film, i.e. a sheet material, having atleast one release surface comprising a release material such as asilicone, polyethylene, fluorocarbon, or polypropylene. The releasesurface can be provided as an integral part of the release liner, or,alternatively, in the form of a separate release layer or coating. Therelease surface imparts to the release liner the surface adhesion andrelease characteristics desired in view of the adhesive to which theliner is to be applied. It also functions to create a coherent surfaceto which the pressure-sensitive adhesive can be laminated.

A preferred embodiment of the release liner comprises (i) a TEO core and(ii) a release layer or coating comprising a release material comprisinga polyethylene, polypropylene, fluorocarbon, or silicone. The releaselayer or coating provides the release surface that contacts theadhesive. The TEO core may be composed exclusively of a TEO, or may be ablend of TEO and one or more other materials such as polyethylene.

In another preferred embodiment, the release liner comprises a mixture,preferably a blend, of TEO and at least one other material, preferably arelease material such as polyethylene or silicone, in proportions so asto provide the release surface as an integral part of the release liner;a separate release coating or layer is not included.

The present release liner is preferably tear-resistant. It preferablyexhibits a low release value from acrylate-based adhesives, as describedbelow, and has high cross web strength. A nick or tear in the releaseliner of the present invention typically will not propagate like a tearin a polyethlyene or polypropylene liner. When present, the releasecoating further reduces stress on the release liner during removal fromthe adhesive.

Also provided by the invention is a method for making a release linerfor use with an adhesive applied to a substrate during a heating andcooling cycle. The method involves fashioning a release liner from amaterial that exhibits thermal expansion and contraction propertiessimilar to those observed for the intended substrate. For example, thecoefficients of thermal expansion and contraction of the substrate canbe measured, and an extrudable material exhibiting similar thermalcoefficients can be selected or fabricated. A film comprising theselected material is extruded, and at least one release surface isprovided on the film for release of the film from the adhesive. Theextruded film is thermally stable under the manufacturing or processingconditions (e.g., a thermal cycle involving exposure to an elevatedtemperature for a defined period of time) to which the intendedsubstrate (after application of the adhesive with liner) will besubjected. Preferably, the intended substrate comprises a TEO, and therelease liner is also formulated from a TEO, preferably an extrusiongrade of the same TEO. In a particularly preferred embodiment of themethod of the invention, the intended substrate is an automobile bodypart comprising TEO.

The present invention further provides a method for using a releaseliner during heating and cooling of an intended substrate. A releaseliner is adhered to a pressure sensitive adhesive, then applied to asubstrate. The substrate is exposed to elevated temperatures for aperiod of time, then returned to room temperature. The release linerdoes not significantly buckle or substantially shrink away from thepressure-sensitive adhesive during the heating or cooling processes, andpreferably remains coextensive with the pressure-sensitive adhesiveafter being returned to room temperature.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Preferred release liners of the invention take the form of a film (i.e.,a sheet material) comprising a thermoplastic elastomeric olefin (TEO).As used herein, the terms release liner, liner, release film and releasesheet are interchangeable. Thermoplastic elastomeric olefins (TEOs),also referred to in the art as thermoplastic polyolefins (TPOs), are aclass of materials which are both thermoplastic and elastic in nature.TEO is typically a blend of a rubbery material, such as, for example, anethylene propylene rubber (such as ethylene-propylene monomer [EPM] orethylene-propylene-diene-monomer [EPDM]), a nitrile rubber, or a styrenebutadiene rubber, with a thermoplastic (such as polypropylene,polyethylene, or polyvinyl chloride), and is often compounded with avariety of additives and fillers, such as carbon black, plasticizers,antidegradants, fillers, and the like. TEO is commercially availabletypically as a blend of polypropylene and EPDM. Alternatively, the TEOcan be formed by copolymerizing a thermoplastic, for examplepolypropylene, with a rubbery material, such as ethylene-propylenerubber. The rubbery material can be either vulcanized or not vulcanized.

The relative proportion of thermoplastic, preferably polypropylene, torubbery material in a TEO can range from about 15% by weightthermoplastic to about 85% thermoplastic, and about 85% rubbery materialto about 15% rubbery material, respectively. The higher the amount ofthermoplastic, the more brittle and the more like a thermoplastic theTEO is. A higher amount of rubbery material will make the TEO closer torubber in characteristics. TEOs are formulated to produce the desiredend-use characteristics. Accordingly, the various TEOs useful for linersin the practice of the invention are selected so as to provide therelease liner with expansion and contraction characteristics that matchor approximate those of the substrate, preferably a TEO substrate, towhich it will be adhered.

Preferably, the TEO used in the release liner comprises from about 30%to about 70% by weight thermoplastic, and about 70% to about 30% rubberymaterial. More preferably, the TEO comprises from about 40% to about 60%by weight thermoplastic, and about 60% to about 40% by weight rubberymaterial. Particularly preferred because of its commercial availabilityis a TEO comprising polypropylene and ethylene propylene rubber. Thepreferred ranges of thermoplastic to rubbery material are particularlysuitable for liners used to protect pressure-sensitive adhesive tapes onTEO substrates such as those used in many current automotive body sidemoldings.

In addition to providing the release liner with increased stability atelevated temperatures and an improved ability to expand and contractupon heating and contract in concert with its intended substrate, TEO asa component of the liner can also impart tear resistance without the useof a woven (fiber) or nonwoven reinforcing layer. This is advantageousbecause the use of other layers can limit the amount of elasticity andflexibility of the liner, and thereby limit the uses of thepressure-sensitive adhesive article.

TEOs useful in the practice of the invention include commerciallyavailable TEOs such as those available under the DEXFLEX trade name fromD & S Plastics Intl. (Auburn Hills, Mich.), those under the ALCRYN tradename available from DuPont Co. (Wilmington, Del.), those under theMULT-FLEX trade name available from Multibase (Copley, Ohio), and thoseunder the POLYTROPE TPP trade name available from A. Schulman (Akron,Ohio). The grade of TEO is selected for the type of processing that willbe used to make the release liner, and is preferably an extrusion grade,such as Dexflex SB-814 available from D & S Plastics Intl. Commerciallyavailable TEOs may include other additives such fillers, processingaids, plasticizers, and the like.

The release liner of the invention can be made by processes that arecommercially known, and available. These processes include blown filmextrusion or coextrusion for films having multiple layers and sheetextrusion or coextrusion. The films can be made in thicknesses of about0.0005 inch to about 0.010 inch, and preferably in thicknesses of about0.001 inch to about 0.008 inch. Generally, thinner films are desired forcost considerations, but it may be necessary to use thicker films toobtain certain properties such as tear resistance, tensile strength, andthe like.

Various additives may be blended into the TEO resin prior to extrusion,or they may be added directly to the extruder. The additives areincluded in typical amounts for the purpose for which they are intended,and include fillers, colorants (e.g., dyes or pigments), slip agents,anti-blocking agents, processing aids, and the like.

Anti-blocking agents are particularly useful for outer layers ofpolyethylene to prevent sticking or blocking between layers ofpolyethylene when the extruded film is wound onto a roll. Usefulmaterials include diatomaceous earth either by itself, or preferably ina low density polyethylene binder. Antiblocking agents are typicallyincluded in amounts of from about 1% to about 20% by weight of thepolyethylene resin, and preferably in amounts of from about 3% to about8%.

Polyethylenes are useful as processing aids to enhance the extrusion andfilm flatness of TEO resins. They can optionally be blended with the TEOto affect the release characteristics of the film. Any type ofpolyethylene may be used, and low density polyethylene and linear lowdensity polyethylene are preferred. The polyethylenes can be used inamounts from about 1% to 99% by weight, and is preferably used inamounts of about 15% or greater.

Colorants (e.g., dyes or pigments) are useful as additives and aretypically used in amounts of about 0.1% to about 5% by weight of thefilm composition, and preferably from about 0.3% to about 3%.

In one embodiment of the release liner of the invention, the TEO isprovided in a film core (referred to herein as a TEO film core or simplyTEO core) to which a release coating or layer is or can be applied. TheTEO core can be exclusively TEO (including, optionally, additives,fillers, and the like), or, alternatively, can be a mixture or blend ofTEO and one or more other polymers such as polyethylene. In thisembodiment, it is not necessary that the polymer with which the TEO isblended to form the TEO core be effective to impart the desired releaseproperties to the film (although it may be), because the release surfaceis provided by the release coating or layer. Preferably, the TEO corecomprises from about 5% by weight to about 100% by weight TEO, and morepreferably from about 10% to about 100% TEO. The selection of therelative amounts of TEO and other polymer is determined by the endproperties needed for the release liner, e.g., tensile strength, tearresistance, etc. The release coating (described in more detail below) isor can be applied to one or both sides of the TEO film core, dependingupon the intended use and the release characteristics desired.Typically, the release coating for this embodiment is in the form of alayer that constitutes about 7% to about 15% of the total thickness ofthe release liner. Where the adhesive is present on a substrate, the TEOcore and the release coating are substantially co-extensive throughoutat least that portion of the liner which is contacted to theadhesive-coated portion of the substrate.

In a second embodiment, the release liner of the invention furthercomprises a release material such as a polyethylene, polypropylene,fluorocarbon or silicone, in such proportion so as to provide therelease surface as an integral part of the release liner. This ispreferably achieved by mixing, preferably by blending, a TEO with atleast one other material selected to impart the desired releaseproperties to the TEO blend when formed into a film; commerciallyavailable TEO typically does not itself provide a suitable releasebecause it adheres too strongly to the adhesive. However, a TEO can beformulated, e.g., by varying the amount of thermoplastic such aspolyethylene or polypropylene, so as to provide an integral releasesurface without the need for blending with another release material. Inthis embodiment of the invention, inclusion of a separate surfacerelease coating or layer is optional.

Suitable materials with which TEO can be mixed to integrate the desiredrelease properties into the release liner of the second embodimentinclude polymers such as polyolefins, preferably polyethylenes andpolypropylenes, and copolymers of ethylene such as ethylene vinylacetate. Preferably, the TEO is mixed with polyethylene. For a releaseliner of the second embodiment that is particularly useful with acrylicadhesives, a polyethylene is blended with TEO in relative amounts ofabout 95% to about 50% by weight polyethylene and about 5% to about 50%by weight TEO, more preferably about 90% to about 60% by weightpolyethylene and 10% to 40% by weight TEO. The preferred blends of TEOand polyethylene provide acceptable release properties from acrylicadhesives without a separate release coating. As the percentage of TEOincreases, and the percentage of polyethylene decreases, thepressure-sensitive adhesive adheres more tightly to the liner andremoval of the liner becomes more difficult. This is particularly trueif the adhesive and liner are heated at an elevated temperature becauseheat tends to promote an increase in adhesion of pressure-sensitiveadhesives to liners.

Useful polyethylenes for both the first and second embodiments includehigh density polyethylenes having a typical density around 0.96 g/cc(grams/cubic centimeter), medium density polyethylenes having a typicaldensity of about 0.93 g/cc to about 0.94 g/cc, low density polyethyleneshaving densities of about 0.90 g/cc to about 0.92 g/cc, linear lowdensity polyethylenes, and very low density polyethylenes havingdensities below about 0.90 g/cc. In general, the higher the density, thehigher the release force needed to remove the liner from apressure-sensitive adhesive. Lower density polyethylenes provide lowerrelease values. The selection of the material depends upon the desiredrelease properties. Polyethylenes of different densities can be blendedtogether, or they can be blended with ethylene co-polymers to providethe desired properties. For example, a blend of high densitypolyethylene with a low density polyethylene can be used to make amedium density polyethylene having intermediate release values betweenhigh and low density polyethylenes.

Another useful polyethylene for use in the TEO mixtures of both thefirst and second embodiments is a very low density polyethylene formedas a copolymer of ethylene and an alpha olefin having from about 3 toabout 10 carbon atoms using a metallocene polymerization catalyst.Suitable alpha-olefins include butene-1, hexene-1, octene-1, andcombinations thereof. The copolymers have a density of less than about0.90 g/cc, preferably less than about 0.89 g/cc, and more preferably,less than about 0.88 g/cc. The copolymers also have a narrow molecularweight distribution as defined by having a polydispersity of about 1 toabout 4, and preferably about 1.5 to about 3.5. The polydispersity isdefined as the ratio of the weight average molecular weight to thenumber average molecular weight. Additionally, the copolymers can becharacterized by a composition distribution breadth index (referred tohereinafter as “CDBI”). The CDBI is defined as the weight percent of thecopolymer molecule having a co-monomer content within 50 percent (i.e.,±50%) of the median total molar co-monomer content. The CDBI and themethod for its determination is described in U.S. Pat. No. 5,206,075,incorporated herein by reference. The CDBI of suitable copolymers ispreferably greater than 70% and more preferably greater than 80%.Suitable copolymers are commercially available from Exxon Chemical Co.under the EXACT tradename and from Dow Chemical Co. under the ENGAGEtrade name.

Release coatings or layers applied to the TEO film core in the firstembodiment preferably include a release material comprising apolyolefin, more preferably polyethylene or polypropylene, that impartsthe desired release characteristics to the liner. Other releasematerials that can be used as coatings or outer layers with the firstembodiment of the release liner include silicones, e.g., polysiloxanes,epoxy silicones, as well as perfluoroethers, fluorocarbons,polyurethanes, and the like. Release materials are known and aredescribed in various sources including patent literature. For example,epoxy silicones are disclosed in U.S. Pat. No. 4,822,687 (Kessel etal.), U.S. Pat. No. 5,217,805 (Kessel et al.), U.S. Pat. No. 5,576,356(Kessel et al.), U.S. Pat. No. 5,332,797 (Kessel, et al.);perfluoropolyethers are disclosed in U.S. Pat. No. 4,830, 910 (Larson),fluorocarbons in a polymer matrix are disclosed in U.S. Pat. No.5,110,667 (Galick et al.) and various types of silicones are describedin U.S. Pat. No. 2,588,367 (Dennett), U.S. Pat. No. 3,960,810 (Chandraet al.), U.S. Pat. No. 4,162,356 (Grenoble), U.S. Pat. No. 4,306,050(Koerner et al.); British Patent No. 1,375,792 (Colquhoun et al.), andGerman Patent No. 2,736,499 (Hockemeyer), each of which is incorporatedherein by reference. Commercially available release materials areavailable from various suppliers such as General Electric Co. (Albany,N.Y.), Dow Corning under to SYL-OFF tradename, (Midland, Mich.), WacherChemie (Germany), and Th. Goldschmidt AC (Germany). Coatings arecommercially available from Akrosil (Menasha, Wis.), and Daubert(Willowbrook, Ill.).

Release materials can be applied to the TEO core as solvent orwater-based coatings, solventless coatings, hot melt coatings, or theycan be co-extruded with the TEO core using conventional processes.Solvent and water-based coatings are typically applied to the TEO coreby processes such as roll coating, knife coating, curtain coating,gravure coating, wound rod coating, and the like. The solvent or wateris then removed by drying in an oven, and the coating is optionallycured in the oven. Solventless coatings include 100% solids compositionssuch as silicones or epoxy silicones which are coated onto the TEO bythe same types of processes used for solvent coating, and then cured byexposure to ultraviolet light. Optional steps include priming the TEObefore coating or surface modification of the TEO such as with coronatreatment. Hot melt coatings such as polyethylenes or perfluoroethersare 100% solids coatings which are heated and then applied through a dieor with a heated knife. Hot melt coatings are preferably applied byco-extruding the release material with the TEO core in blown film orsheet extruder for ease of coating and for process efficiency.

The TEO core can be coated on one or both sides to provide a releaseliner of the first embodiment. The amount of release force, e.g., theforce required to remove the liner from the adhesive, can range fromalmost zero to about 60 ounces per inch width (oz/in). When the releaseforce is on the higher end of the range, i.e., above about 50 oz/in, itis difficult to start removal of the liner as well as to continueremoval of the liner once a part of the liner has been removed from theadhesive. With high removal forces, the liner can tear or the adhesivemay be pulled away from the intended substrate causing distortion orwrinkling of the adhesive and adversely affecting the adhesive holdingpower. The lower end of the removal force range, e.g., less than about 5oz/in is typically known as the “premium release” and these values areusually obtained with silicone coatings. At times, premium release maynot be desired if the liner releases too easily and pops off of theadhesive to expose the adhesive to dirt and other contamination. Releasevalues of about 15 to about 45 oz/in are suitable for most applicationsso that the liner adheres well enough to the adhesive to avoid poppingoff while remaining easily removable.

The release surface of the release liner of the invention thuspreferably exhibits a release value of less about 60 oz./inch, morepreferably less than about 45 oz./inch, most preferably less than about30 oz./inch, as measured in the Release Force Test Method describedbelow. Where the release material comprises a silicone, the releasevalue of the release surface of the liner is preferably less than about10 oz./inch, more preferably less than about 5 oz/inch.

When both sides are coated, the coatings on each side may be the same orthey may be different to provide a differential release. Fordifferential release, the release liner will have a higher release forceon one side than the other. For example, one side of a release liner maybe coated with a silicone release material having a release force from apressure sensitive adhesive of 10 ounces/inch (oz/in) and the other sidemay have a silicone release material having a release force of 20 oz/in.This ensures that the adhesive will adhere more tightly to one side ofthe liner than the other so that when a roll of tape is unwound, theadhesive consistently stays on the same side of the release liner.

The liner of the invention is useful for any type of pressure-sensitiveadhesive used in the industry. This includes pressure-sensitiveadhesives based on acrylate or acrylics, polyesters, silicones, blockcopolymers, ethylene vinyl acetate, and the like. The selection of therelease surface will depend upon the type of pressure-sensitive adhesiveto which it is adhered. For example, release surfaces of polyethylene,polypropylene, perfluoroethers, and silicone are useful with acrylatepressure-sensitive adhesives, and perfluoroethers are useful forsilicone pressure-sensitive adhesives.

Useful pressure sensitive adhesives in the practice of this inventioninclude acrylic adhesives, natural rubber adhesives, tackified blockcopolymer adhesives, polyvinyl acetate adhesives, ethylene vinyl acetateadhesives, silicone adhesives, polyurethane adhesives, thermosettablepressure-sensitive adhesives such as epoxy acrylate or epoxy polyesterpressure-sensitive adhesives, and the like. These types ofpressure-sensitive adhesives are known in the art and are described inthe Handbook of Pressure Sensitive Adhesive Technology, Satas (Donatas),1989, 2^(nd) edition, Van Nostrand Reinhold, as well as the patentliterature. The pressure sensitive adhesives may also include additivessuch as cross-linking agents, fillers, gases, blowing agents, glass orpolymeric microspheres, silica, calcium carbonate fibers, surfactants,and the like. The additives are included in amounts sufficient to effectthe desired properties.

The release liner of the invention is preferably used with aheat-stable, pressure-sensitive, adhesive. Heat stable,pressure-sensitive adhesives include acrylate pressure-sensitiveadhesives such as, for example those described in Re 24906 (Ulrich),U.S. Pat. No. 4,181,752 (Martens et al.), U.S. Pat. No. 4,818,610(Zimmerman et al.) and silicone pressure-sensitive adhesives. Theadhesives can be prepared by any of the known methods including emulsionpolymerization, solvent polymerization, e-beam polymerization,ultraviolet light polymerization, and the like. Typically, acrylateadhesives are homopolymers and copolymers of monofunctional unsaturatedacrylic or methacrylic acid ester monomers of non-tertiary alcoholshaving from about 1 to about 20 carbon atoms, and preferably from about4 to about 12 carbon atoms. A co-monomer may optionally be included toimprove the cohesive strength of the adhesive. Such reinforcingco-monomers useful in making the copolymers typically have a higherhomopolymer glass transition temperature than the glass transitiontemperature of the acrylic acid ester homopolymer.

Suitable acrylic acid ester monomers include 2-ethylhexyl acrylate,isooctyl acrylate, isononyl acrylate, n-butyl acrylate, decyl acrylate,dodecyl acrylate, octadecyl acrylate, and mixtures thereof. Preferredmonomers include isooctyl acrylate, n-butyl acrylate, and mixturesthereof.

Useful reinforcing co-monomers include acrylic acid, methacrylic acid,itaconic acid, acrylamide, substituted acrylamides, N-vinyl pyrrolidone,N-vinyl caprolactam, isobornyl acrylate, and cyclohexyl acrylate.Preferred co-monomers include acrylic acid, N-vinyl caprolactam, andisobornyl acrylate.

In a typical process to make pressure sensitive adhesive transfer tapes,an adhesive composition is coated onto a release liner. The adhesive isthen cured to form a gelled film on the liner, and the release linerwith the adhesive is rolled up into a large roll. Alternatively, theadhesive may be coated and cured on one liner, and then transferred ontoa different liner before converting. The adhesive coated sheet is thenconverted into narrow rolls by slitting the large roll and winding thenarrow width tape onto cores for customer use. The liners of theinvention can also be used with foam tapes such as 5605 and 5344 AcrylicFoam Tapes available from Minnesota Mining & Manufacturing Co. (St.Paul, Minn.), as well as double coated tapes.

The release liner of the invention is preferably thermally stable (i.e.,stable to heat), that is, it retains structural integrity insofar as itwill not melt or decompose significantly at elevated temperatures usedin the manufacturing or processing of an intended substrate. A preferredrelease liner retains structural integrity when exposed to temperaturesof about 90° C., more preferably about 120° C., most preferably about150° C., for a period of about 20 minutes, more preferably for a periodof about one-half hour, most preferably for a period of about one hour.

The release liner of the invention preferably exhibits substantially noshrinking or buckling when brought to room temperature after beingexposed to an elevated temperature for an extended period of time. Apreferred liner exhibits substantially no shrinking or buckling whenbrought to room temperature (i.e., about 20-25° C.) after being exposedto a temperature of about 90° C., more preferably about 120° C., mostpreferably about 150° C., for a period of about one-half hour, morepreferably about one hour. Shrinking and buckling can be avoided byselecting a release liner having thermal expansion and contractioncoefficients substantially similar to those of the intended substrate.The coefficients of thermal expansion and contraction of the releaseliner are preferably within at 10% of the thermal expansion andcontraction coefficients of the intended substrate or article to whichan adhesive film comprising the liner is applied.

Although preferred embodiments of the release liner of the invention arethermally stable, tear-resistant, and/or exhibit substantially noshrinking or buckling when brought to room temperature after beingexposed to an elevated temperature for an extended period of time, it isto be understood that the present invention is not to be unnecessarilylimited. Accordingly, any release liner for use with a pressuresensitive adhesive, which release liner comprises a TEO, is within thescope of the present invention.

The following non-limiting examples further illustrate the presentinvention. Unless otherwise indicated, the following test procedureswere used in the examples. The particular materials and amounts thereofrecited in these examples, as well as other conditions and details, areto be interpreted to apply broadly in the art and should not beconstrued to unduly restrict or limit the invention in any way.

Test Methods

Release Force

Samples are prepared by laminating the release side or surface of theliner to the adhesive side of a pressure-sensitive adhesive tape (5344Acrylic Foam Tape Minnesota Mining & Manufacturing Co., St. Paul, Minn.)using a hand roller to eliminate air pockets. The other side of the tapeis protected with a standard polyethylene release liner. Stripsmeasuring 2.54 cm wide by 17.8 cm long are cut and then aged for 3 daysat room temperature (about 20-25° C.) and tested, or aged at 70° C. for7 days and tested. To test, the standard polyethylene liner is removedand the adhesive tape is laminated to the bed of an IMASS AdhesionTester (Imass Inc. Hingham, Mass.). The liner is then pulled away fromthe adhesive at a 180 degree angle and a speed of 30 cm/minute. Theforce required to remove the liner is reported in ounces/inch (oz/in).

Tear Resistance

A 5.08 cm by 15.24 cm sample of the liner is cut with the 5.08 cmdimension being the minor axis and the 15.24 dimension being the majoraxis. The major axis is the test direction (downweb or crossweb). A 1.9cm notch is cut from one edge at the middle of the minor axis andparallel to the major axis of the sample. The sample is placed in anINSTRON Tensile Tester (Instron Corp, Canton, Mass.) having a 2.54 cmjaw separation such that the notch is positioned in line with the jaws.The jaws are separated at a speed of 19.7 cm per minute and the averageforce required to tear the sample is recorded. Samples are run in boththe downweb direction and the crossweb direction. The test results arerecorded in pounds.

Expansion and Contraction on a TEO Substrate

The substrate used in this example is an injection molded thermoplasticpolyolefin (DEXFLEX 777, D & S Plastics Intl., Auburn Hills, Mich.) bodyside molding obtained from Lexamar (Boyne City, Mich.). The molding isabout 4 feet in length. The release liner is laminated to an adhesivetape (5344 Acrylic Foam Tape), and a 32 inch long strip of adhesive tapewith the release liner is applied to the molding. The molding is thenheated at 149° C. for 30 minutes, and then cooled to room temperature.The liner is examined for wrinkling or buckling, and whether or not theliner has shrunk and left exposed adhesive at the ends of the tape.

EXAMPLE 1

A film was prepared by extruding a blend of 85 parts of TEO(thermoplastic elastomeric olefin) and 15 parts of LLDPE (linear lowdensity polyethylene), and about 1 part of a red pigment (PM4532available from Techmer, Clinton, Tenn.) to a thickness of 0.153 mm thickusing a blown film extruder. The TEO was a thermoplastic polyolefinhaving fillers and constituting a 50/50 blend of polypropylene and EPDM(ethylene propylene diene monomer). It was obtained as DEXFLEX SB-814from D&S Plastics Intl. (now Solvay Engineered Plastics, Auburn Hills,Mich.). The LLDPE was a linear low density polyethylene available asESCORENE LD117.85 from Exxon Chemical Co. (Houston, Tex.). The blownfilm extruder was run to achieve sufficiently high melt flowtemperatures to provide a uniform flat film. Extruder temperaturesranged from about 177° C. to about 205° C. The film was then coated oneach side with ultraviolet cured silicone compositions available fromAkrosil to make a release liner. Specifically, one side of the compositewas coated with H2C (Akrosil), which has a low release value, and theother side was coated with H3B (Akrosil), which has a higher releasevalue. The release liner was tested for release force on the H3B side.The release force after 3 days at room temperature (about 20-25° C.) was0.96 oz/inch, and after 7 days at 70° C., the release force was 2.3oz/inch. The liner was tested for expansion and contraction on a TEOsubstrate as described in the Test Methods above. It did not exhibit anyvisible shrinkage or wrinkling.

EXAMPLE 2

A 0.153 mm thick film composite was prepared by coextruding 0.127 mm ofTEO (DEXFLEX SB-814) having about 1% red pigment (PM4532) as a core,0.013 mm of LDPE (low density polyethylene) on one surface of the TEO,and 0.013 mm of MDPE (medium density polyethylene) on the other surfaceof the TEO, on a blown film extruder. The low density polyethylene had adensity of 0.92 g/cc and was obtained under the tradename PETROTHENENA353 from Quantum Chemical Corp (Cincinnati, Ohio). The medium densitypolyethylene had a density of about 0.93 g/cc and was a blend of 33parts by weight LDPE (PETROTHENE NA353) and 67 parts high densitypolyethylene having a density of 0.96 g/cc. It was obtained under thetradename PETROTHENE LT6180 from Quantum Chemical Corp. The medium andlow density polyethylenes provided differential release surfaces for anacrylate pressure-sensitive adhesive. The release liner was tested fortear strength. The liner had a machine direction tear strength of 0.5pounds and a cross direction tear strength of 4.9 pounds. The liner wastested for expansion and contraction on a TEO substrate as described inthe Test Methods above. It did not exhibit any visible shrinkage orwrinkling.

EXAMPLES 3-6

A release liner was prepared by blending TEO (DEXFLEX SB-814), withvarying amounts of a low density polyethylene as shown in Table 1, andforming a 0.153 mm thick film using a blown film extruder. The TEO wascolored with a carbon black pigment. The polyethylene was DOWLEX 2045which is a linear low density polyethylene having a density of 0.92 g/ccand a narrow molecular weight distribution. The liners were tested forrelease force as described above except that the samples were aged in anoven at 121° C. for 30 minutes and cooled to room temperature beforetesting. The release values are shown in Table 1. The data show that inthe preferred ranges of TEO and polyethylene (Examples 5 and 6),acceptable release values (i.e., under about 40 oz/inch) are obtained.All of the liners were tested for expansion and contraction on a TEOsubstrate using the Test Method described above. None of them exhibitedany visible shrinkage or wrinkling. TABLE 1 TEO/LDPE Blends ExampleParts TEO Parts LDPE Release Force oz/in 3 80 20 55.4 4 60 40 65.2 5 2080 39.4 6 10 90 29.1

The complete disclosure of all patents, patent documents, andpublications cited herein are incorporated by reference. The foregoingdetailed description and examples have been given for clarity ofunderstanding only. No unnecessary limitations are to be understoodtherefrom. The invention is not limited to the exact details shown anddescribed, for variations obvious to one skilled in the art will beincluded within the invention defined by the claims.

1. A method for making a release liner for use with a pressure-sensitiveadhesive applied to a substrate during a heating and cooling cyclecomprising: (a) extruding a film comprising a selected material thatexhibits thermal expansion and contraction properties similar to thoseexhibited by the substrate; and (b) providing at least one releasesurface on the film for release of the film from the adhesive.
 2. Themethod of claim 1 wherein the substrate comprises thermoplasticelastomeric olefin (TEO).
 3. The method of claim 1 wherein the selectedmaterial comprises thermoplastic elastomeric olefin (TEO).
 4. The methodof claim 1 wherein the selected material comprises polyethylene.
 5. Themethod of claim 1 wherein the material is selected by comparing thecoefficients of thermal expansion and contraction of candidate materialswith the coefficients of thermal expansion and contraction of thesubstrate.
 6. The method of claim 1 wherein the release surface isprovided by coating a release material onto a surface of the film. 7.The method of claim 6 wherein the release material comprises silicone.8. The method of claim 6 wherein the release material comprisespolyethylene.
 9. A method for using a release liner comprising: (a)applying a pressure-sensitive adhesive adhered to a release liner to asubstrate; (b) heating said substrate having the pressure-sensitiveadhesive and release liner adhered thereto; and (c) cooling saidsubstrate having the pressure-sensitive adhesive and release lineradhered thereto; such that the release liner does not significantlybuckle or substantially shrink away from the pressure-sensitiveadhesive.